Holographic laser scanning system employing holographic scanning disc having dual-fringe contrast regions for optimized laser beam scanning and light collection operations

Abstract

Holographic laser scanning system employing a holographic scanning disc with holographic facets having dual-fringe contrast regions optimized for scanning and light collection operations. In the preferred embodiments, the first region of each holographic facet is optimized for laser light having a first polarization state, whereas the second portion thereof is optimized for laser light having a second polarization state. The dual-fringe contrast scanning disc construction of the present invention provides for improved laser scanning efficiency during scanning operation, and improved laser light collection efficiency during laser light collection/detection operation within the system.

What is claimed is: 
     
       1. A holographic laser scanning system comprising: a laser scanning disc rotatable about an axis of rotation and having a plurality of holographic optical elements for scanning a laser beam and producing a laser scanning pattern for scanning code symbols, each said holographic optical element having dual-fringe contrast regions including a first region characterized by a first fringe contrast optimized for scanning said laser beam across a code symbol in said laser scanning pattern, and   a second region characterized by a second fringe contrast optimized for collecting light reflected off said code symbol scanned by said laser beam during scanning operations.     
     
     
       2. The holographic laser scanning system of claim 1, wherein said laser scanning disc has an outer radius and an inner radius, and said first regions are located adjacent said outer radius and said second regions are located adjacent said inner radius. 
     
     
       3. The holographic laser scanning system of claim 2, which further comprises a plurality of laser beam sources for producing a plurality of laser beams for transmission through said holographic elements as said laser scanning disc rotates about said axis of rotation. 
     
     
       4. The holographic laser scanning system of claim 3, wherein said first regions of said holographic optical elements are optimized for laser light having a first polarization state, and said second regions of said holographic optical elements are optimized for laser light having a second polarization state. 
     
     
       5. A method of constructing a holographic scanning disc having one or more holographic optical elements for scanning a laser beam and producing a laser scanning pattern for scanning code symbols, said method comprising the steps of: (a) for each said holographic optical element, making a first portion of said holographic optical element with a first modulation index and   (b) making the second portion of said holographic optical element with a second modulation index which is different than said first modulation index.   
     
     
       6. The method of claim 5, wherein step (a) comprises exposing a layer of photosensitive material to a first object beam and a first reference beam having relative intensities which result in the formation of the first portion of said selected holographic optical element having said first modulation index, and wherein step (b) comprises exposing a layer of photosensitive material to a second object beam and a second reference beam having relative intensities which result in the formation of the second portion of said selected holographic optical element having said second modulation index. 
     
     
       7. The method of claim 5, wherein step (a) comprises making said first portion of each said holographic optical element optimized for laser light having a first polarization state, and wherein step (b) comprises making said second portion of each said holographic optical element optimized for laser light having a second polarization state.